Speakers

A loudspeaker is any transducer capable of transforming electrical energy into acoustic energy.

This transformation can be based on various physical principles, the most commonly used of which are :

• the electrodynamic principle: any conductor placed in a uniform magnetic induction field B and carrying a current is the seat of an electromagnetic force;

• the electrostatic principle: the two plates of a planar capacitor through which an alternating current flows are subject to an attractive force proportional to the electrical charge of the plates and the inter-electrode electric field;

• the piezoelectric principle: a piezoelectric material subjected to an electric field undergoes a deformation proportional to the electric polarization;

• the electromagnetic principle: an air gap of variable width (and hence reluctance) placed in a magnetic circuit through which a flux induced by a coil flows is subject to an attractive force on its armatures that is roughly proportional to the current flowing through the coil;

• the ionic principle: a mass of air ionized by an HF electrical discharge between two electrodes generates a local variation in pressure proportional to the thermal agitation induced by the LF modulation of the electrodes.